Prior art systems for conveying articles (e.g., workpieces such as substrates, or workpiece containers such as substrate carriers or FOUPs) through a transport path within a fabrication facility may include a cradle upon which conveyed articles may be loaded. Such systems stop at different process tools to load or unload substrate carriers from the cradles or tools as needed. Typically the cradles come to rest and a robotic arm using an end effector removes a carrier from a cradle or loads a carrier on a cradle.
In prior art systems where the cradle pivots freely on the conveyor or is otherwise allowed to move on the conveyor belt, the orientation of the carrier may be determined by, for example, a controller of the robotic arm when the carrier is removed. However, such systems are not suitable to be used as a continuously moving, high-speed conveyor system due to the time it may take for the carrier to stop rotating (or otherwise moving), the time it may take to determine the carrier orientation, and the time required to remove the carrier from the cradle.
In prior art conveyor systems where the cradle is rigidly mounted to the conveyor, the conveyor system may be designed to tolerate the stresses that the cradle and the conveyor exert on each other as the cradle is moved through turns on the transport path. Such systems may be designed to function for at least a minimum acceptable time before the inherent stresses result in a failure of a component of the system. Such systems thus require regular maintenance to replace fatigued parts. Thus, such systems are not suitable to be used as a continuously moving, high speed conveyor system because of the maintenance requirement.
Therefore, systems and methods are needed to mount cradles to conveyors that are suitable for use in continuously moving, high speed transport systems.